a. Field of the invention:
The present invention is concerned with a ski of the hollow core assembly type having a centrally longitudinally extending hollow structure sandwiched between two flanking members.
B. Description of the prior art:
As a means of improving the function and operability of skis, there has been the concept to reduce the total weight of the ski as much as possible.
In order to attain this reduction of the total weight of the ski, there has been practiced in general to provide a ski having a hollow-structured core assembly which constitutes the main part of the ski and which is comprised generally of a central core member and flanking members sandwiching the central core member therebetween. However, it is presently considered quite difficult in the ski manufacturing industry to form a hollow structure within the core assembly, as considered from its relation with the ski top and bottom constituting units which are to be laminated on the top and bottom sides of the core assembly, respectively. A brief description will hereunder be made on the known manner of forming a hollow structure within the core assembly of a ski. As shown in FIG. 9, a central core member 1 made of a glass fiber-reinforced plastic (which will hereinafter to be referred to briefly as FRP) and cross-sectionally having a U-shaped channel is provided to extend longitudinally in the central part of the ski. On the lateral sides of this central core member 1 are provided flanking members 2 and 2 made of a material such as a foamed hard polyurethane resin, wood pieces or honeycomb. The central core member 1 and the flanking members 2 and 2, in combination, constitute a core assembly 3. To the extreme lateral sides of this core assembly 3 are firmly secured side members 4 and 4, and to the top side of the core assembly 3 is firmly laminated a ski top constituting unit which is comprised of a top plate 5 made of FRP, top edges 6 and 6 and a ski surface decorating member 7. To the bottom side of the core assembly 3 is firmly laminated a ski bottom constituting unit which is comprised of a bottom plate 8 made of FRP, sole edges 9 and 9 and a gliding surface member 10. This cross-sectionally U-shaped central core member 1 has, accordingly, a longitudinally extending channel of a U-shaped cross section and its opening is covered with the top plate 5 made of FRP, thereby presenting a hollow portion 11 in the ski. It should be noted that, in a conventional ski having the aforesaid core assembly arrangement, the plane of bonding between the end edges of the opening of the U-shaped central core member 1 and the top plate 5 made of FRP tends to be broken or become separated apart relative to each other by the concentrated application, to this plane of bonding, of considerable amounts of shearing forces caused by the impacts and vibrations which occur during the operation of the ski. Thus, such a ski can be said to be exposed to a great deal of danger during its use and to be poor in its mechanical strength and short in its service life. Moreover, when, at the time of manufacture of such a ski, it is intended to laminate the top plate 5 made of FRP onto the core assembly 3 by bonding them together, it is mandatory that this top plate 5 of FRP be made with separately prepared semi-hardened resin-impregnated sheets, i.e., prepreg sheets, and therefore, there occurs the inconvenience that, during the heat-pressing step at the time of forming the whole core assembly, the FRP resin of the top plate oozes into the space in the U-shaped channel of the central core member 1, adversely affecting the formation of a desirable neat shape of the U-shaped channel, causing a subtle disorder of the structural balance of the ski as a whole.